Temperature control for magnetron filament



Nov. 11, 1941. LA VERN QP ILPQTT ,2

TEMPERATURE CONTROLFORlMAGNETRON FILAMENT Filed March 2, 1938 2 Sheets-Sheet 1 0S0 PLATE 8 FILAMENT SUPPLY all] 05C. SU PPLY IN VEN TOR.

Zia Vrne R. Phil 005i BY ATToRN E Y BLOCKING was SUPPLY 2 Sheets-Sheet 2 UPPLV Filed March 2, 1938 LA VERNE R. PHILPOTT CARBON PILE TEMPERATURE CONTROL FOR MAGNETRON FILAMENT MAGNETRON SUPPLY MAGNETRON SUPPLY Nov. 11, 1941.

lpott M/K SUPPLY OSC.

INVENTOR La Vr'ne R. Phi BY ATTORNEY Patented Nov. 11, 1 941 TEMPERATURE CONTROL Eon MAGNETRON FILAMENT La Yerne R.Philpott, Washington, D. 0. Application March: 2, 1938, SerialNo. 193,546

r 9 Claims. (01. 250-27) (Granted under the act of'March 1883, as

amended April 30, 1928; 370 0. G. 757) This invention relates to apparatus that functions as a thermostatic control upon the temperature of a magnetron tube filament to maintain that temperature uniform and thereby attain constancy of operation of the magnetron.

Among the several objects of this invention are:

To provide means to prevent variations of the filament current from an optimum value during operation;

To provide means to secure the optimum flow of current through a magnetron filamentwhen for any reason that current doesnot have the optimum value as, for example, at the beginning of operation of the tube;

To maintain the electron emission in netron within prescribed limits;

To improve generally the operation of magnetrons and increase the useful life thereof.

In the drawings: i

Fig. 1 illustrates means for utilizing the IR. drop resulting from the passage of the magnetron "anode current through a resistor, to control the filament current supply; 2

Fig. 2 is in general similar to Fig. 1 but a single tube, having a dual function, replaces twotubes in the current supply in Fig. 1; 1

Fig. 3 depicts the use of a photoelectric cell energized by light from the filament to produce a current that is applied .to control netron filament supply; e

Fig- 4 illustrates how the effective value-of a variable resistance in series with the filament is changed by the anode-cathode current ofthe magnetron;

the magthe mag--.

through the .filament, no oscillations are generated until the anode voltage reaches almostthe final point and at that time the filament temperature rises suddenly, often to the point of destroying the filament. The present invention provides means for automatically reducing the filament current before damage is done by the above mentioned sudden and inordinate rise of the filament temperature. 2

Referring to Fig. 1, the anode 6 of magnetron oscillator tube '1 is supplied from a suitable source 8 through high frequency choke 9. The cathode it of tube 1 is heated by current from transformer secondary ll throughleads l2 enclosed in grounded shielding l3 through high frequency chokes M. The filament current is derived from an oscillator unit comprising a tube I4 suitably connected to the oscillatory network l5 whereof Grid 20 of tube [4 is coupled to an oscillator tank circuit [5 by condenser 2| and is biased by resistor 22 through choke 23. The plate and filament supply for tube [4 is derived fromthe unit 24.- The anode-cathode circuit of magnetron 1 includes the conductor 25 connected to a center tap of secondary H and a portion of resistor 26 that serves as a biasing resistor for grid I1 of tube 18. The, usual by-pass-condensers 2 1 are provided where desired. It ;is'-,ap-

, parent that, the magnetron supply 8 having-been Fig. 5 shows schematically the use ofa resistance-capacitance bridge whereof the filament of the magnetron is one arm, which bridge .is balanced when the filament has thecorrect temperature, and unbalance of. the bridgeacts to.

cause a change in the filament current that will restore the balance.

It is to be understood that the present'invention may be utilized to control the operation of a magnetron oscillator either within prescribed limits or in an arbitrary manner according to certain desired conditions of operation. The

conventional circuits such as the coils for producing the magnetic field ina magnetron oscillatory circuit have beenomitted from the drawings for:

the purpose of simplification. It is very essential that close control be exercised over the temperature of the filament in a magnetron oscillator, since as the anode voltage thereof is raised from zero, with initially. 'normal current flowing connected into the magnetron circuit, when the oscillator unit is setinto operation current will be supplied from the oscillator-l4 through condenser by current to heat the cathode] 0 will be induced .in transformer secondary ll. 'Whenthe operating conditions of magnetron l'have been reached current will flow from the cathode l0 through secondary l! and conductor 25 to resistor 26 and ,in the portion of that resistor included inthe anode-cathode circuit of magnetron 1 there will be produced an IR drop proportional to the anode-cathode current of the magnetron and this drop will be impressed upon; grid I! of tube I8,

thereby reducing the output of tube [8" and. diminishing the current supplied to filament I0.

when the returned current is flowing through the magnetron.

g The embodiment of my invention shown in Fig.

-of photocell 36. ment' Ill increases the output of photocell 36 rises 'and thereby produces an increased potential difference across resistance 39 to the high poten- 2 is essentially similar to that illustrated in Fig. 1, with the difference that a dual purpose tube is utilized to replace the tubes I4 and I8 of Fig. 1. Here the tube 28 serves both as the master oscillator and as the transferring tube. The grid 29 functions as the anode and the grid 36 functions as the control grid for producing oscillations in the network 3| and these oscillations are simultaneously impressed upon the electron stream through tube 28, and the output is connected to transformer secondary by the tuned primary circuit IS. The anode-cathode current from magnetron '1 passes through conductors 3.2 and 33 to resistor 34 and the potential drop resulting therefrom is applied to the grid 36 to control the output of the tube. Resistor 35 has the same biasing function as does resistor 22 in Fig. 1.

The apparatus disclosed in Fig. 3 is very similar to that in Fig. 2 and the same reference characters have been applied to corresponding parts. However, it has been found that in some cases undesirable results follow from changing the anode-cathode potential of the magnetron the intensity of that light, as is well-known. A blocking tube 31 has its anode connected between 'bi'asing resistor 34 and grid 30 of tube 28, thus including the resistor 34 in the anode-cathode circuit of'the tube 31. The current flows from "cathode 38 of photocell 36 through resistor 39 thence through bias supply 46, blocking tube supply M and oscillator supply 24 back to anode 42 As the temperature of the filatial' end of which grid 43 of blocking tube 31 is connected, and thus greater current flow from the photocell 36 results in increased current through'blocking tube 31 and increased potential drop across resistor 34 which swings grid 30 of tube 28 more negative and cuts down the current supply to filament Hi.

In Fig; 4 the current for filament I6 is derived A spring 46 acts upon member 4'! to passes through a solenoid 48 acting upon mem- 'ber 4'| in opposition to spring 46 to increase the resistance of carbon pile 45. "the resistance in the filament circuit of mag- ][t is apparent that netron I will be increased as the anode-cathode current of the magnetron rises and thus the filament current is held to a value within the desiredoperating conditions.

This modification also, as in Fig. 3, provides control of the filament temperature without variation of the anodecathode potential of the magnetron.

In Fig. the filament H) of magnetron I is 3 one arm of a resistance-capacitance bridge hav- --ing"a capacitance 49 in one arm, capacitance 56 in another arm and the'resistance 5| in still another arm. Connected across the bridge in the well-known manneris a coil 52 in parallel with a variable-capacitance 53, the coil 52' being coupledto coil 54 that is connected between grid 55 and cathode 56 of a tube 5T whereof the anode 58 is connected to a tank circuit 59 coupled to tuned input 60 of a tube 6|. The anode 62 of tube 6| is connected to one terminal of a center-tapped transformer primary 63. Anode 64 of oscillator 65 is connected to the other terminal of primary 63 which is coupled to secondary- 66 that supplies current to filament ll] of magnetron The values of the elements making up the bridge in the circuit of filament l0 are so chosen that when the filament is at the proper temperature the bridge is balanced and no current flows through coil 52. However, when the temperature of filament I6 is too low the bridge becomes unbalanced and the input into tube 51 from coil 52 is such that tube 6| is caused to pass current in such phase that it is additive in primary 63 with the output from oscillator 65, thereby increasing'the current flowing through filament I6 and raising the temperature thereof but, on the other hand, if the temperature of filament I0 is too high the unbalance of the bridge phases the output of 6| to buck the output of tube 65 and so reduce the current supplied to the filament.

The invention herein described and claimed may be used and/or manufactured by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising a transformer secondary coil in series with said cathode, a vacuum tube having a cathode, a grid and an anode, a tuned output circuit connecting the cathode and the anode of said vacuum tube including a transformer primary coil coupled with said secondary, a circuit operatively connecting the grid and the cathode of said vacuum tube including a grid sistor whereby to reduce the output of said vacuum tube proportionately to the current between the anode and the cathode of said magnetron, a vacuum tube oscillator network, and means operatively connecting the output of said oscillator to the grid of said vacuum tube.

2. The combination with a magnetron tub having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising a transformer secondary coil in series with said cathode, a vacuum tube oscillator network, means to transfer energy from said oscillator to said secondary including a tuned transformer primary, means operatively connecting the anode of said magnetron to the midpoint of said secondary including a resistance so connected and related to the aforesaid energy transfer means that the potential drop due to the passage of anode current from said magnetron through said resistance diminishes the transfer of energy tosaid secondary in proportion to said potential drop.

.3. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising a transformer secondary coil in series with said cathode, a vacuum tube oscillator network, means to transfer energy point of said secondary including a resistance so connected and related to the aforesaid energy transfer means that the potential drop due to the passage of anode current from said magnetron through said resistance diminishes the transfer of energy to said secondary in proportion to said potential drop.

4. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising a transformer secondary coil in series with said cathode, an oscillatory network including a vacuum tube having an anode, a cathode and a control grid, an output coil coupled to said secondary, and a resistance connecting 7 said anode to said cathode; a blocking tube having an anode, a grid and a cathode, an output circuit connecting said anode and said cathode, said output circuit including said resistance whereby anode current of said blocking tube negatively biases the grid of said tube in the oscillatory circuit; a photo-electric cell disposed to be excited proportionately to the temperature of the cathode of said magnetron, and means connecting said photo-electric cell to impress a positive bias upon the grid of said blocking tube proportionately to the current from said photoelectric cell.

5. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising a transformer secondary coil in series with said cathode, a capacitanceresistance bridge whereof said cathode is one arm, said bridge being balanced when said cathode has the proper operating temperature, a

circuit including a coil and a variable capacitance in parallel connected across said bridge to be energized when said bridge is unbalanced, a transformer primary coupled to said secondary, an oscillatory network including a vacuum tube having a plurality of electrodes and an anode connected to one terminal of said primary, a second vacuum tube connected to the other terminal of said secondary, common supply means for both said vacuum tubes, a third vacuum tube coupled to said parallel connected coil whereby the output of said third vacuum tube is controlled by said parallel connected coil, and means connecting said third vacuum tube to said second vacuum tube whereby the output of said second vacuum tube is controlled by said third vacuum tube, the phase of energization of said parallel connected coil when said bridge is unbalanced being such that the output of said second vacuum tube is additive to or subtractive from the output of said first vacuum tube in said primary, to control the current through the cathode of said magnetron to maintain the temperature of said cathode substantially constant.

6. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising means including a voltage controlled discharge device through which all heating energy for said cathode passes to supply to said cathode an alternating heating current, means traversed by the anode-cathode current of said magnetron to develop a potential difference proportional'to said anode-cathode current, and means to apply said potential difierence as a potential difference directly to said discharge device to control said heating current to maintain said anode-cathode current substantially constant.

7. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising means including a voltage controlled discharge device through which all heating energy for said cathode passes to supply to said cathode a heating current, means traversed by the anode-cathode current of said magnetron to develop a potential difference proportional to said anode-cathode current, and means to apply said potential difference as a potential difference directly to said discharge device to control said heating current to maintain said anode-cathode current substantially constant.

8. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising means to supply heating current to the cathode of said magnetron, a photo-cell disposed to be excited by light from said cathode, a vacuum tube, said photo-cell being connected to increase the output of said vacuum tube as the output of said photo-cell increases, and means connecting said vacuum tube to said supply means whereby the output of said supply means is decreased by increased output of said vacuum tube.

9. The combination with a magnetron tube having an anode and a cathode, of apparatus to control the temperature of said cathode during operation, comprising means to supply heating current to the cathode of said magnetron, a vacuum tube, means responsive to the intensity of light from said cathode to supply current proportional to said intensity connected to said vacuum tube to increase the output of said vacuum tube as the output of said light responsive means increases, and means connecting said vacuum tube to said heating current supply means whereby the output of said heating current supply means is decreased by increased output of said vacuum tube.

LA VERNE R. PHILPOTT. 

